1. Field of the Invention
The present invention relates to a method for manufacturing flat glass in which the glass is formed while being supported on the surface of a pool of molten metal. More particularly, the invention relates to a method for introducing protective atmosphere gases into a chamber in which the glass is formed.
2. Summary of Related Art
In a variety of processes, a continuous ribbon of glass is formed while supported on and advancing along the surface of a pool of molten metal. In general, a protective reducing atmosphere is created in a head space above the advancing glass ribbon and the supporting pool of molten metal in order to prevent the oxidation of the molten metal and, consequently, the contamination of the glass. Patents illustrating the use of such a protective atmosphere in glass making operations include: U.S. Pat. No. 3,594,143 to Mohyuddin; U.S. Pat. No. 3,551,126 to Sacrez et al.; U.S. Pat. No. 3,423,197 to Loukes, et al.; U.S. Pat. No. 3,462,253 to Seusi; U.S. Pat. No. 3,356,476 to Gulotta; U.S. Pat. No. 3,337,319 to Edwards; U.S. Pat. No. 3,337,322 to Taylor; U.S. Pat. No. 3,630,701 to Javaux; U.S. Pat. No. 3,970,442 to Gulotta; U.S. Pat. No. 3,976,460 to Kompare, et al.
All of these patents show the introduction or migration of protective atmosphere gases into a head space overlying an advancing continuous ribbon of glass supported on a pool of molten metal.
It is common practice to introduce protective gases of varying compositions into different portions of the service space or plenum above the roof of a glass forming chamber, so that controlled amounts of protective gases flow down through the permeable roof at different locations along the length of the chamber. For example, Taylor, in U.S. Pat. No. 3,337,322, shows the introduction of a protective gas comprising from 0.25 to 3.0 percent hydrogen in nitrogen into a plenum, or service space, near the inlet end of a chamber while introducing a protective gas comprising from 3.0 to 10 percent hydrogen in nitrogen into the plenum near the outlet end of the chamber.
Further, in U.S. Pat. No. 3,970,442, Gulotta discloses the introduction of a reducing gas such as hydrogen directly into the headspace of a glass forming chamber at locations generally well downstream from the inlet or hot end where the molten glass is fed to the forming chamber. In addition, an inert gas such as nitrogen is introduced into the service space or plenum of the forming chamber which is separated from the headspace by a permeable roof.